1. Field of the Invention
The invention relates to a recording and reproducing apparatus and, more particularly, to a recording and reproducing apparatus for recording and reproducing a plurality of pieces of two-dimensional information to a holographic recording medium in which multiplex recording can be performed in the same physical region.
2. Description of the Related Art
A holographic recording medium is a medium capable of recording two-dimensional information of a large amount, for example, a few megabytes on a page data unit basis in the form of a hologram.
The same physical region on a medium is irradiated with information light associated with user data to be recorded and reference light, and interference fringes of the information light and the reference light are recorded. Consequently, the holographic recording medium has an advantage that a number of pieces of page data are multiplexedly recorded on the same physical region by changing, for example, an incident angle to a medium and wavelength of the reference light (see Japanese Unexamined Patent Application No. 2004-158114).
Since a large amount of user data on recorded in a single physical recording region in a medium, there is an advantage that information of a larger amount can be recorded as compared with conventional recording media such as a CD and a DVD.
As such holographic recording media, a so-called write-once medium on which information can be written only once and which cannot be rewritten, and a rewritable medium are developed.
For the purpose of reproducing information as a three-dimensional image, a holographic stereogram recording medium is used.
The holographic stereogram is obtained by recording a sequence of parallax images captured from different observation points in the horizontal direction so as to be continuous in the horizontal direction. At the time of reproduction, the images are seen like a three-dimensional image by parallax which occurs when an observer views the images.
On a medium on which such holographic stereogram is recorded, not only an image recorded as so-called write-once hologram, supplemental information such as sound information at the time of creation, creation conditions, date and time, and place is recorded (see Japanese Unexamined Patent Application No. Hei 11-344918 (1999)).
The supplemental information is recorded in a region different from that of an image by a recording method of magnetic recording, optical recording or the like.
On the holographic stereogram recording medium, a plurality of images of different view points are recorded so as to be viewed three-dimensionally. Although the supplemental information can be additionally recorded, an image itself recorded as a hologram cannot be additionally recorded and multiplex recording of user data aiming at large-amount recording cannot be performed. The supplemental information is preliminarily determined and a large amount of information such as image data cannot be newly added to the recording region of the supplemental information.
In a holographic recording medium for multiplexedly recording a large amount of user data by using information light and reference light, the minimum recording unit is a page of a few megabytes. It can be said that use efficiency of the medium is high in the case of recording user data of about the minimum recording unit.
In the case of holographic-recording document data of a small amount (tens Kbytes) of tens of pages of A4-size into one page, only a small region in one page as the minimum unit is used and the rest of the page becomes a vacant region. In spite of the large recording capacity, there is a case that the use efficiency of the medium is very low.
Due to the characteristics of the holographic recording, data cannot be additionally recorded in part of one page, and only part of data recoded in the page cannot be rewritten.
For example, in the case of rewriting only part of a page, first, all of a recorded region in the page has to be erased.
Particularly, in the case where a plurality of pieces of page data (P1, P2, . . . , and Pn) are multiplexedly recorded on the same region A, it is impossible to select and erase only one page data (for example, P2) including data desired to be rewritten. Therefore, a series of processes have to be performed in which all of the multiplexedly recorded page data (P1, P2, . . . , and Pn) is reproduced once and temporarily stored in another memory, all of the pages (P1, P2, . . . , Pn) in the region A are erased, the page data P2 is rewritten to page data P2′ including desired rewrite data, and the new page data P2′ and the other page data (P1, P3, . . . , and Pn) temporarily stored is re-recorded on the same region A.
That is, in the case where only data of one line in a page out of user data of a large amount such as hundreds of pages is desired to be rewritten, only the data in the line cannot be rewritten. The series of processes of reproduction, temporary recording, all erasure, data rewriting, and re-recording have to be performed on also page data which does not have to be rewritten. It takes long time to perform the rewriting process and it causes deterioration in performance of the recording function of the apparatus.
Therefore, although the process of recording and reproducing data onto/from the holographic recording medium has the advantage that a large amount of data can be recorded and reproduced at once in short time, when the medium is used in such a manner that a small amount of data is recorded or rewritten frequently, the use efficiency of the medium is low, it takes long time for rewriting, and the recording performance deteriorates.